Hi, It seem that in the ContextDoItScope>>#emitPrologue: you should have: emitPrologue: methodBuilder Preferences compileBlocksAsClosures ifTrue: [ self hasEscapingEnv ifFalse: [^ self]. self emitCreateEnv: methodBuilder. self emitMoveCapturedRargs: methodBuilder. ] Is it true? (Preferences compileBlocksAsClosures ifTrue: is missing) Math